Gas diffusion layer for fuel cell, comprising spun carbon nanofiber layer

ABSTRACT

The present invention relates to an electrolyte membrane including a nanofiber spun layer for a fuel cell, a membrane-electrode assembly including the electrolyte membrane, and a fuel cell including the membrane-electrode assembly.

TECHNICAL FIELD

The present invention relates to an electrolyte membrane including a nanofiber spun layer for a fuel cell, a membrane-electrode assembly including the electrolyte membrane, and a fuel cell including the membrane-electrode assembly.

This application claims the benefit of Korean Patent Application No. 10-2017-0080431 filed on Jun. 26, 2017, and the entire contents of which are incorporated herein by reference.

BACKGROUND ART

A fuel cell is an electrochemical cell that converts chemical energy produced by oxidation of fuel into electrical energy. Recently, various investigations have focused on the development of fuel cells as well as solar cells and the like in order to overcome problems such as consumption of fossil fuels, the greenhouse effect and global warming caused by carbon dioxide, and the like.

A fuel cell generally converts chemical energy into electrical energy through oxidation and reduction of hydrogen and oxygen. In the fuel cell, hydrogen is oxidized into hydrogen ions and electrons at an anode, and the hydrogen ions diffuse to a cathode through an electrolyte. The electrons travel to the cathode through a circuit. At the cathode, water is produced through reduction of the hydrogen ions, electrons, and oxygen.

The electrolyte membrane is disposed between the cathode and the anode to serve as a hydrogen ion carrier and to prevent contact between oxygen gas and hydrogen gas. Therefore, the electrolyte membrane of the fuel cell is required to have high hydrogen ion conductivity and high mechanical and chemical stability.

Conventionally, an electrolyte membrane in which a fluorine-based ionomer is coated on a sulfone-based polymer membrane or a hydrocarbon-based polymer membrane has been used as an electrolyte membrane.

However, such a conventional electrolyte membrane dose not have excellent thermal conductivity to have a problem in that the power generation efficiency is lowered, and that the mechanical stability and chemical stability of the sulfone-based polymer membrane or the hydrocarbon-based polymer membrane have not reached satisfactory levels.

DISCLOSURE Technical Problem

The present invention is to provide an electrolyte membrane for a fuel cell which has a uniform pore distribution and a high porosity while exhibiting excellent heat transfer efficiency to have excellent power generation efficiency, a membrane-electrode assembly including the electrolyte membrane and a fuel cell including the membrane-electrode assembly.

Technical Solution

The present invention provides an electrolyte membrane for a fuel cell.

Further, the present invention provides a membrane-electrode assembly for a fuel cell, the assembly including: an electrolyte membrane; and an anode electrode and a cathode electrode facing each other with the electrolyte membrane interposed therebetween, in which each of the anode electrode and cathode electrode includes a gas diffusion layer and a catalyst layer.

Further, the present invention provides a fuel cell including: a stack including one or more of the membrane-electrode assemblies and a separator interposed between the membrane-electrode assemblies; a fuel supply unit for supplying fuel to the stack; and an oxidant supply unit for supplying an oxidant to the stack.

Advantageous Effects

The electrolyte membrane according to the present invention has a high porosity and a uniform pore distribution to have excellent heat transfer efficiency so that the water content of the electrolyte membrane is maintained at an appropriate level, and thus the membrane-electrode assembly and the fuel cell including the same exhibit excellent power generation efficiency.

Further, the electrolyte membrane according to the present invention has excellent mechanical stability and chemical stability due to the non-conductive nanofiber spun layer which is not subjected to a carbonization process such as heat treatment.

DESCRIPTION OF DRAWINGS

FIG. 1 is a photograph of the microstructure of the nanofiber spun layer produced according to Production Example 1 in Experimental Example 1, taken with a field emission scanning electron microscope at a magnification of 10 k.

FIG. 2 is a photograph of the microstructure of the electrolyte membrane produced according to Comparative Example 1-1 in Experimental Example 1, taken with a field emission scanning electron microscope at a magnification of 10 k.

FIG. 3 illustrates a current-voltage curve obtained by measuring the current-voltage values of each unit cell according to Examples 1-2 to 4-2 in Experimental Example 2.

MODE FOR INVENTION

Hereinafter, the electrolyte membrane for a fuel cell according to the present invention is described.

The electrolyte membrane for a fuel cell according to the present invention includes a nanofiber spun layer.

The nanofiber spun layer according to the present invention is formed by electrospinning a polymer composition.

In one embodiment of the present invention, the electrospinning is performed by applying a voltage of 30 kV to 70 kV, more preferably a voltage of 40 kV to 60 kV, during the spinning of the polymer composition. If the voltage is less than 30 kV, the splitting of the fibers is not actively performed, and the volatility of the solvent is lowered. If the voltage exceeds 70 kV, a tip-trouble occurs at the tip of the nozzle through which the polymer composition is spun.

In one embodiment of the present invention, the electrospinning is performed at a temperature of 40° C. to 80° C., preferably a temperature of 50° C. to 80° C. If the temperature at which the electrospinning is performed is less than 40° C., the viscosity of the polymer solution becomes high to prevent the polymer from being spun smoothly. Therefore, it may not ensure mass productivity. If the temperature at which the electrospinning is performed is more than 80° C., the solvent is volatilized in the polymer solution so that the composition of the polymer solution may be changed. Further, the pressure in the solution tank due to solvent volatilization may increase, resulting in risk of explosion.

In one embodiment of the present invention, the fiber of the electro-spun nanofiber spun layer has the average diameter of 0.01 μm to 2 μm, more preferably 0.02 μm to 1 μm. If the average diameter of the fiber is less than 0.01 μm, the size of the gap between the fibers decreases to reduce the gas permeability. If the average diameter of the fiber exceeds 2 μm, the size of the gap between the fibers increases so that the foreign substances present in the gas pass through the gap to accumulate in the cell stack, resulting in a decrease of the performance as the electrolyte membrane of the fuel cell.

In one embodiment of the present invention, the electrospinning is performed by applying pressure to the container while a voltage is applied between a tip which is an opening of the container storing the polymer composition and a current collecting plate spaced apart from the tip in the gravity direction.

In one embodiment of the present invention, the spacing distance between the tip and the current collecting plate is 10 cm to 20 cm, preferably 12 cm to 16 cm. If the spacing distance is less than 10 cm, the residual solvent is left, and the nanofibers are melted due to the residual solvent, resulting in the desired nanofiber deformation. When the spacing distance exceeds 20 cm, the magnetic field formation between the current collecting plates becomes unstable so that the nanofiber layer is not formed.

In one embodiment of the present invention, the polymer composition includes at least one selected from the group consisting of a polyacrylic resin such as polymethyl methacrylate (PMMA), polystyrene (PS), polyacrylic acid (PAA) and polyacrylonitrile (PAN); a polyvinyl resin such as polyvinyl chloride (PVC), polyvinyl alcohol (PVA) and polyvinyl acetate (PVAc); a polyester resin such as polyethylene terephthalate (PET), polytrimethylene terephthalate (PTT), and polybutyleneterephthalate (PBT); Nylon; polycarbonate, polyethylene oxide (PEO); polyurethane (PU), polyvinylidene fluoride (PVdF); poly(vinylidene fluoride)-co-(hexafluoropropylene) [P(VDF-HFP)]; poly(vinylidene fluoride)-co-(chlorotrifluoroethylene) [P(VDF-CTFE)], polytetrafluoroethylene-co-hexafluoropropylene-co-vinylidene fluoride (THV); polyether ether ketone, poly phenylene oxide (PPO); poly phenylene sulfone (PPS); polysulfone (PS); poly ether sulfone (PES); polyimide (PI); polyether imide (PEI); polyamide imide (PAI); polybenzimidazole (PBI); polybenzoxazole (PBO); and polyaramid.

In one embodiment of the present invention, the nanofiber spun layer has a thickness of 20 μm to 200 μm, more preferably 50 μm to 150 μm. When the thickness of the nanofiber spun layer is less than 20 μm, the physical properties of the nanofiber spun layer deteriorate during the heat treatment. When the thickness of the nanofiber spun layer is more than 200 μm, the amount of the membrane-electrode assembly of the gas separation layer after the heat treatment is limited.

Hereinafter, a method for producing an electrolyte membrane for a fuel cell according to the present invention is described. Unless otherwise specified, the description of the electrolyte membrane for a fuel cell as described above can be applied to the following method for producing an electrolyte membrane for a fuel cell.

The method for producing an electrolyte membrane for a fuel cell according to the present invention includes the step of electrospinning a polymer composition and forming a nanofiber spun layer.

The step of forming the nanofiber spun layer includes the step of applying a voltage of 30 kV to 70 kV, more preferably of 40 kV to 60 kV, during spinning of the polymer composition.

In one embodiment of the present invention, the step of electrospinning includes the step of applying pressure to the container while a voltage is applied between a tip which is an opening of the container storing the polymer composition and a current collecting plate spaced apart from the tip in the gravity direction.

Hereinafter, the membrane-electrode assembly for a fuel cell according to the present invention is described.

The membrane-electrode assembly for a fuel cell according to the present invention includes an electrolyte membrane for the fuel cell; and an anode electrode and a cathode electrode positioned opposite to each other with the electrolyte membrane interposed therebetween.

In one embodiment of the present invention, the electrolyte separator may be formed of a perfluorosulfonic acid polymer, a hydrocarbon-based polymer, polyimide, polyvinylidene fluoride, polyethersulfone, polyphenylene sulfide, polyphenylene oxide, polyphosphazene, polyethylene naphthalate, polyester, doped polybenzimidazole, polyether ketone, polysulfone, an acid thereof or a base thereof.

Each of the anode electrode and the cathode electrode according to the present invention includes a gas diffusion layer and a catalyst layer.

In one embodiment of the present invention, the catalyst layer of the anode electrode may include at least one catalyst selected from the group consisting of platinum, ruthenium, osmium, platinum-ruthenium alloy, platinum-osmium alloy, platinum-palladium alloy and platinum-transition metal alloy.

In one embodiment of the present invention, the catalyst layer of the cathode electrode includes platinum.

In one embodiment of the present invention, the catalyst of the anode electrode or the cathode electrode is supported on the carbon-based carrier.

Hereinafter, the fuel cell according to the present invention is described.

The fuel cell according to the present invention includes: a stack including the membrane-electrode assembly and a separator interposed between the membrane-electrode assemblies; a fuel supply unit for supplying fuel to the stack; and an oxidant supply unit for supplying an oxidant to the stack.

The separator according to the present invention serves to prevent the membrane-electrode assemblies from being electrically connected, to transfer the fuel and oxidant supplied from the outside to the membrane-electrode assembly, and serves as a conductor for connecting between the anode electrode and the cathode electrode in series.

The fuel supply unit according to the present invention serves to supply fuel to the stack and may include a fuel tank for storing the fuel and a pump for supplying the fuel stored in the fuel tank to the stack.

In one embodiment of the present invention, the fuel is hydrogen or hydrocarbon fuel in a gaseous or liquid state.

In one embodiment of the present invention, the hydrocarbon fuel is methanol, ethanol, propanol, butanol or natural gas.

The oxidant supply unit according to the present invention serves to supply the oxidant to the stack.

In one embodiment of the present invention, the oxidant is oxygen or air.

In one embodiment of the present invention, the oxidant is injected with a pump.

In one embodiment of the present invention, the fuel cell is a polymer electrolyte-type fuel cell or a direct methanol-type fuel cell.

Hereinafter, the present invention is described in more detail by way of Examples. However, these Examples are intended to illustrate the present invention only, and the scope of the present invention is not limited by these Examples.

<Production Example 1> Production of Nanofiber Spun Layer

800 g of dimethylacetamide (DMAc) was added to 200 g of polyvinylidene fluoride (PVDF) and dissolved to produce a polymer spinning solution (the solution's concentration: 20% by weight).

Thereafter, 6 ml of the produced polymer spinning solution was input into the polymer composition supply container of the electrospinning device manufactured by Oseong Technology Co. from Korea. Then, the distance between the tip, which is the opening of the supply container, and the current collecting plate spaced apart from the tip in the gravity direction, was set to 15 cm, a voltage of 30 kV was applied between the tip and the current collecting plate while the temperature in the supply container was controlled to be 70° C. as a constant temperature, and the polymer spinning solution of the supply container was sprayed with pressure for 8 hours, thereby obtaining the nanofiber spun layer having a width of 25 cm, a length of 45 cm and a thickness of 100 μm.

<Production Example 2> Production of Nanofiber Spun Layer

A nanofiber spun layer was produced in the same manner as in Production Example 1 except that the temperature in the supply container for the polymer spinning solution of the electrospinning device was controlled to be 45° C. as constant temperature.

<Production Example 3> Production of Nanofiber Spun Layer

A nanofiber spun layer was produced in the same manner as in Production Example 1 except that the temperature in the supply container for the polymer spinning solution of the electrospinning device was controlled to be 35° C. as constant temperature.

<Production Example 4> Production of Nanofiber Spun Layer

A nanofiber spun layer was produced in the same manner as in Production Example 1 except that the temperature in the supply container for the polymer spinning solution of the electrospinning device was controlled to be 25° C. as constant temperature.

<Example 1-1> Production of Electrolyte Membrane

The nanofiber spun layer produced in Production Example 1 was impregnated into an ion conductor in which a polymer of PFSA series was dispersed in a solvent mixed with water and alcohol at a ratio of 1:1, thereby producing an electrolyte membrane.

<Example 2-1> Production of Electrolyte Membrane

An electrolyte membrane was produced in the same manner as in Example 1-1, except that the nanofiber spun layer produced in Production Example 2 was used as a nanofiber spun layer.

<Example 3-1> Production of Electrolyte Membrane

An electrolyte membrane was produced in the same manner as in Example 1-1, except that the nanofiber spun layer produced in Production Example 3 was used as a nanofiber spun layer.

<Example 4-1> Production of Electrolyte Membrane

An electrolyte membrane was produced in the same manner as in Example 1-1, except that the nanofiber spun layer produced in Production Example 4 was used as a nanofiber spun layer.

<Example 1-2> Production of Unit Cell

The carbon paper as a gas diffusion layer was superimposed on both sides of the electrolyte membrane produced in Example 1-1. In order to maintain gas sealing property around the membrane-electrode assembly, a 210 μm gasket adhered to the polymer electrolyte portion excluding the electrode portion, and the anode plate having a flow path for supplying hydrogen and uniform pressure and the cathode plate for supplying air and uniform pressure to the membrane-electrode assembly were adhered to the membrane-electrode assembly, thereby producing the unit cell.

<Example 2-2> Production of Unit Cell

A unit cell was produced in the same manner as in Example 1-2, except that the electrolyte membrane produced in Example 2-1 was used as an electrolyte membrane.

<Example 3-2> Production of Unit Cell

A unit cell was produced in the same manner as in Example 1-2, except that the electrolyte membrane produced in Example 3-1 was used as an electrolyte membrane.

<Example 4-2> Production of Unit Cell

A unit cell was produced in the same manner as in Example 1-2, except that the electrolyte membrane produced in Example 4-1 was used as an electrolyte membrane.

<Experimental Example 1> Observation of Microstructure Via FE-SEM

The microstructures of the nanofiber spun layer produced according to Production Example 1 and the nanofiber spun layer produced according to Production Example 4 were photographed using a field emission scanning electron microscope (FE-SEM) with a trade name of SU-70, manufactured by Hitachi, Ltd. The photographs are illustrated in FIGS. 1 and 2, respectively.

The results of observing the microstructure of the nanofibers according to the present invention indicate that the diameters of the fibers were different depending on whether the temperature of the polymer spinning solution was controlled in a certain range during the production of the nanofiber spun layer. As a result, it can be confirmed that when a certain temperature is not maintained during electrospinning, a portion of the nanofibers is dissolved in the solvent due to insufficient residual solvent volatilization.

<Experimental Example 2> Measurement of Performance of Unit Cell

In order to compare the performance of the fuel cells according to the present invention, the performance of the unit cells was measured under the following conditions.

Relative humidity: 80%

Cell temperature: 65° C.

Gas supply: anode—hydrogen/cathode—air

Measurement device: fuel cell performance TEST STATION by CNL Co.

Surface area of electrolyte membrane: 25 cm²

First, current-voltage values of the unit cells according to Examples 1-2 to 4-2 were measured, and thus current-voltage curves are illustrated in FIG. 3. Specifically, each current density of unit cell at 0.6 V is shown in Table 1 below.

TABLE 1 Unit cell Current density of 0.6 V (mA/cm²) Example 1-2 900 Example 2-2 800 Example 3-2 740 Example 4-2 710

As illustrated in FIG. 3, it is confirmed that fuel cells of Examples 1-2 and 2-2 using electrolyte membranes produced by applying a voltage while maintaining the temperature of the polymer spinning solution in the supply container at 45° C. and 70° C., respectively during the production of electrolyte membrane have superior power generation performance than those of Examples 3-2 and 4-2 using electrolyte membranes produced by applying a voltage while maintaining the temperature of the polymer spinning solution in the supply container at 35° C. and 25° C., respectively. Further, it is confirmed that the fuel cell of Examples 1-2 has further superior power generation performance than that of Examples 2-2.

Particularly, the fuel cell of Example 1-2 showed the current density at 0.6 V of 900 mA/cm², indicating that the power generation of Example 1-2 is 27% higher than that of Example 4-2 having the current density of 710 mA/cm². 

1. An electrolyte membrane comprising: a nanofiber spun layer for a fuel cell, wherein the nanofiber spun layer is formed by electrospinning a polymer composition.
 2. The electrolyte membrane according to claim 1, wherein the electrospinning is performed by applying a voltage of 30 kV to 70 kV.
 3. The electrolyte membrane according to claim 1, wherein the electrospinning is performed at a temperature of 40° C. to 80° C.
 4. A membrane-electrode assembly for a fuel cell, the assembly comprising: an electrolyte membrane; and an anode electrode and a cathode electrode facing each other with the electrolyte membrane interposed therebetween, wherein each of the anode electrode and the cathode electrode includes a gas diffusion layer and a catalyst layer, and wherein the electrolyte membrane is the gas diffusion layer for a fuel cell.
 5. A fuel cell comprising: a stack including one or more membrane-electrode assemblies and a separator interposed between the membrane-electrode assemblies; a fuel supply unit for supplying fuel to the stack; and an oxidant supply unit for supplying an oxidant to the stack. 